The goal of this proposal is to understand the mechanisms involved in the maternal control (cytotype) of P element transposition in the fruit fly, Drosophila melanogaster. P element transposition is the cause of a syndrome of genetic traits known as hybrid dysgenesis. These traits include high rates of sterility and mutation, as well as chromosomal rearrangements and abnormal germline development. P element transposition can be controlled genetically in crosses where P element-bearing females (P strains) are mated to P strain males. Normally hybrid dysgenesis only occurs when P strain males are mated to females lacking P elements (M strains). P strain females produce eggs that are said to possess "P cytotype" or the ability to repress P element transposition, whereas eggs from M strain females possess the permissive "M cytotype." P cytotype shows an unusual pattern of inheritance through the female germline. The molecular basis of the maternal effect and inheritance of P cytotype will be investigated using P element-mediated transformation, genetic assays for P element repression and P element mRNA and protein localization. Germline transformation will be used to generate Drosophila strains carrying modified P element transposons engineered to express the 66kD P element repressor protein during oogenesis and to localize the 66kD protein mRNA to the posterior germline precursor (pole) cells. Genetic assays will be used to monitor P cytotype repressor activity of these transformants relative to normal P strains. RNA in situ hybridization and antibody staining will be used to correlate expression of the 66kD mRNA and protein during oogenesis with the maternal effect and inheritance of P cytotype repression. The relative levels of the 66kD and transposase mRNAs in purified germline precursor (pole) cells will be determined using the polymerase chain reaction (PCR).